1. Field of the Invention
The invention relates generally to higher voltage output drivers of electronic circuits and in particular to slew rate controlled driver circuits within regulator loops realized with integrated-circuit technologies.
2. Description of the Prior Art
Special output driver circuits in electronic applications are required, when it comes to driving heavier loads, e.g. electromechanical devices such as relays, small motors (AC, DC, or stepping), or other types of sensors and actuators. Another application area is the driving of signals in data bus systems, especially when higher signal voltages on those bus systems are required e.g. when noisier electrical environments have to be taken into account. In this context a reduction of Electromagnetic Interference (EMI) phenomena is important too. These are noted quite common requirements for electronic parts as used in the automotive industry, for example.
Realizations of the prior art for such output driver circuits are often implemented as specifically tailored semiconductor circuits, fulfilling the operational demands regarding the higher voltages and augmented currents needed. Furthermore these drivers have to be interconnected with some logic circuitry, which is controlling the overall operation of the driver circuits, mostly in conjunction with closed loop feedback regulator systems. These logic circuits or even microprocessor systems normally are working with low voltages. The composition of these two voltage domainsxe2x80x94one for higher, the other for lower voltagesxe2x80x94has to be made in such a way, that no detrimental influences are affecting onto each other. Thereto an appropriately combined semiconductor technology capable of handling all these demands is chosen, which most often leads to costly solutions.
Another problem to solve concerning these driver circuits is the sensing and control of the slew rate of the generated signals within the regulator loop. The governing reference is the value of the slew rate, which is generated as an internal reference ramp. This reference ramp is usually generated between the rails of the external output range. In consequence the regulator is fed with the reference ramp for the value required and the driver output signal as the instantaneous signal value. This conception however requires the whole circuit to operate within the high-voltage domain and needs therefore high-voltage drivers and regulator circuits.
It is a challenge for the designer of such circuits to achieve a high-quality, low-cost solution. Several prior art inventions referring to such solutions describe related technologies, methods and circuits.
U. S. Pat. No. (6,181,193 to Coughlin, Jr.) describes using thick-oxide CMOS devices to interface high voltage integrated circuits, especially a high voltage tolerant CMOS input/output interface circuit. In this circuit, a process feature called xe2x80x9cdual-gatexe2x80x9d or xe2x80x9cthick-oxidexe2x80x9d process is used on any devices that will be exposed to high voltage. The thick-oxide devices have a larger capacitance and lower bandwidth, and therefore, preferably, they are only used where exposure to high voltage can cause damage. The remaining devices on the interface circuit may all use a standard process with the thinner oxide, allowing the I/O and the core IC to run at maximum speed. The circuit design topology also limits the number of devices that are exposed to high voltage. Preferably, the protection scheme is broken down into two parts: the driver and receiver.
U.S. Pat. No. (6,201,417 to Blum et al.) discloses the shaping of a current sense signal by using a controlled slew rate, a method and circuit for reducing the leading edge spike in a current sense signal. The current sense signal is a measure of the current through a switched power device controlled by a switching regulator controller. The slew rate of the current sense signal is limited to prevent the slew rate from exceeding a predetermined maximum. The limited slew rate signal is provided to the switching regulator controller. A transconductance amplifier may be used to limit the slew rate of the current sense signal. A capacitor at the output of the transconductance amplifier contributes to controlling the maximum slew rate of the amplifier. The capacitor is charged by the current output of the amplifier to provide a voltage signal for use in place of the original current sense signal. A switch may be provided for selecting between the slew rate limited current sense signal and the original current sense signal. A time delay may be used to control the switch so that the slew rate limiting is replaced by the original current sense signal after a first predetermined time portion of each xe2x80x9con cyclexe2x80x9d of the switched power device.
U.S. Pat. No. (6,476,654 to Tanaka) shows a slew rate adjusting circuit. An interface circuit includes a slew rate control unit, a pre buffer unit, and a main buffer unit. The slew rate control unit is configured as a current source circuit of the pre buffer unit. The slew rate control unit provides a constant current value by using a loop circuit that consists of a slew rate control macro, a decoder, a comparator, N transistor, an external terminal resistance (Rref), and a reference voltage (Vref). A size of the N transistor is adjusted based on a code gradually changed in the loop circuit, and finally the current value is determined uniquely.
U.S. Pat. No. 6,483,386 (to Cress, et al.) discloses a low voltage differential amplifier with high voltage protection. An apparatus comprising a native device coupled to an input of an amplifier. The native device is configured to provide a high voltage protection in response to an enable signal.
A principal object of the present invention is to provide an effective and very manufacturable method and circuit for a slew rate controlled driving of loads for higher voltages and currents.
Another further object of the present invention is to attain a secure cooperation of circuits working in different voltage domainsxe2x80x94a high and a low one.
Another main object of this invention is to reduce EMI phenomena as much as possible, e.g. by slope smoothing.
Also an object of this invention is to transfer the slope destination of the slew rate controlled signal from the high-voltage domain to the low-voltage domain.
Another object of this invention is to avoid the need for destination of absolute signal values by using a differential method for the slope detection.
Another still further object of the present invention is to reach a stable behavior of the regulator circuit, i.e. to attain an unconditional stability of the regulator loop.
A still further object of the present invention is to reduce the power consumption of the circuit by realizing inherent appropriate design features.
Another further object of the present invention is to reduce the cost of manufacturing by implementing the circuit as a monolithic integrated circuit in low cost CMOS technology.
Another still further object of the present invention is to reduce cost by effectively minimizing the number of expensive components.
In accordance with the objects of this invention, a method for realizing a stable high-voltage front-end for an output driver circuit, insensitive against supply voltage variations is given. Said method includes providing a slope transformer circuit, a differentiator with clock, a regulator consisting of a comparator with clock and a digital regulator part, and further a digital-to-analog converter. The method also comprises providing an output driver circuit driving an external load. Also included in said method is transforming a high-voltage input signal in relation to a static high supply voltage level into a proportional current signal, then mirroring this current signal and transforming back linearly into a voltage signal within a low voltage domain as proportional output signal. Equally included in said method is performing a differentiation transaction upon said low voltage output signal, in relation to given time steps from a clock generator. Also incorporated within said method is converting a low voltage differentiated output signal into a digital bit-signal by using a comparator, feeding said bit-signal into a digital regulator part. The comparator together with said digital regulator part builds a regulator. Said comparator is clocked and compares a reference input signal with said differentiated output signal. The comparator can be either a single-output comparator which then generates a bit stream output and uses a single reference value for comparison or a window comparator which then generates bit-outputs corresponding to the reference windows. Said bit outputs of said comparator are fed as input into the digital regulator part which generates an output signal. Finally comprises said method feeding said output signal from said digital regulator as input to a digital-to-analog converter and further the output of the analog-to-digital-converter as input to the output driver circuit, closing a regulator loop with said output signal from an output driver by feeding it back into said high voltage input signal; and in parallel driving an external load with a high voltage output from said output driver.
Also in accordance with the objects of this invention, a circuit, capable of driving higher loads for higher voltages and higher currents with slew rate controlled output signals is achieved. Said circuit comprises means for transforming a high voltage input signal in relation to a static high supply voltage level into a proportional current signal. Also comprised in said circuit are means for mirroring said resulting current input signal into a current output signal and means for generating a low voltage output signal representing said current output signal. Further realizes said circuit means for performing differentiation transactions upon said low voltage output signal, in relation to given time steps and means for converting said low voltage differentiated output signal into a digital bit signal by using a comparator. Said circuit then includes means for feeding said bit signal into a digital regulator part as input and generate an output signal. Still further comprised are means for feeding said output signal from said digital regulator as input to a digital-to-analog converter and generate an analog output. Said analog output feeds the input of the output driver circuit and means for closing a regulator loop with said output signal from said output driver by feeding it back into said high voltage input signal and finally means for driving an external load with said high voltage output from said output driver.